Generally, a chip resistor having a resistor film formed on an insulating substrate in the form of a chip has a drawback that its resistance is likely to change when surge voltage generated due to the influence of static electricity or power supply noise is applied. It is known that the change of resistance due to surge voltage can be suppressed by increasing the length of the current path in the resistor film.
The Patent Documents 1 and 2 as the prior art disclose chip resistors designed to improve the surge resistance.
Specifically, as shown in FIG. 13, the chip resistor 1′ disclosed in the Patent Document 1 includes an insulating substrate 2′ in the form of a chip, terminal electrodes 3′ and 4′ formed on the upper surface of the insulating substrate at longitudinally opposite ends thereof, and a resistor film 5′ having a width W and formed by screen printing on the upper surface of the insulating substrate 2′ to extend longitudinally of the insulating substrate 2′ between the terminal electrodes 3′ and 4′. In screen printing the resistor film 5′, a first and a second longitudinally opposite end edges 5a and 5b of the resistor film 5′ are electrically connected to the terminal electrodes 3′ and 4′ throughout the width W of the resistor film 5′. Further, the resistor film 5′ includes a first inward groove 7′ extending from a first longitudinal edge 5c′ toward a second longitudinal edge 5d′ of the resistor film 5′ and a second inward groove 8′ extending from the second longitudinal edge 5d′ toward the first longitudinal edge 5c′, which are formed in screen printing the resistor film. Specifically, the first inward groove 7′ and the second inward groove 8′ are provided approximately at the longitudinal center of the resistor film 5′ and arranged adjacent to each other so that the first inward groove 7′ is positioned closer to the second end edge 5b′ of the resistor film 5′ than the second inward groove is, whereas the second inward groove 8′ is positioned closer to the first end edge 5a′ of the resistor film 5′ than the first inward groove is.
Further, between the first end edge 5a′ and the second inward groove 8′ of the resistor film 5′ is further provided a first trimming groove 9′, which is formed by e.g. laser beam irradiation to extend from the first longitudinal edge 5c′ toward the second longitudinal edge 5d′. Similarly, between the second end edge 5b′ and the first inward groove 7′ of the resistor film 5′ is provided a second trimming groove 10′, which is formed by e.g. laser beam irradiation to extend from the second longitudinal edge 5d′ toward the first longitudinal edge 5c′. Due to the provision of the two inward grooves 7′, 8′ and the two trimming grooves 9′, 10′, the resistor film 5′ has a winding shape. In this way, the length of the current path in the resistor film 5′ is increased as much as possible.
The chip resistor 21′ disclosed in the Patent Document 2 has such a structure as shown in FIG. 14. Specifically, the chip resistor includes an insulating substrate 22′ in the form of a chip, terminal electrodes 23′ and 24′ formed on the upper surface of the insulating substrate 22′ at longitudinally opposite ends thereof, and a resistor film 25′ having a width W and formed by screen printing on the upper surface of the insulating substrate 22′ to extend longitudinally of the insulating substrate 22 between the terminal electrodes 23′ and 24′. In screen printing the resistor film, a first narrow portion 26′ is provided integrally at the first end edge 25a′ of the resistor film 25′. Of a first and a second longitudinal edges 25c′ and 25d′ of the resistor film 25′, the first narrow portion 26′ is provided at the first longitudinal edge 25c′, and the first end edge 25a′ is electrically connected to the terminal electrode 23′ through the first narrow portion 26′. Further, in screen printing, a second narrow portion 27′ is provided integrally at the second end edge 25b′ of the resistor film 25′. The second narrow portion 27′ is provided at the second longitudinal edge 25d′ of the resistor film, and the second end edge 25b′ is electrically connected to the terminal electrode 24′ through the second narrow portion 27′. Further, the resistor film 25′ includes a first inward groove 28′ formed adjacent to the second end edge 25b′ of the resistor film 25′ to extend from the second longitudinal edge 25d′ toward the first longitudinal edge 25c′, and a second inward groove 29′ formed adjacent to the first end edge 25a′ of the resistor film 25′ to extend from the first longitudinal edge 25c′ toward the second longitudinal edge 25d′, which are formed in screen printing the resistor film 25′.
Further, a first trimming groove 30′ is provided between the two inward grooves 28′ and 29′ of the resistor film 25′ and at a position offset toward the first inward groove 28′. The first trimming groove is formed by e.g. laser beam irradiation to extend from the second longitudinal edge 25d′ toward the first longitudinal edge 25c′. Further, a second trimming groove 31′ is provided between the two inward grooves 28′ and 29′ of the resistor film 25′ and at a position offset toward the second inward groove 29′. The second trimming groove is formed by e.g. laser beam irradiation to extend from the second longitudinal edge 25d′ toward the first longitudinal edge 25c′ Due to the provision of the two inward grooves 28′, 29′ and the two trimming grooves 30′, 31′, the resistor film 25′ has a winding shape. In this way, the length of the current path in the resistor film 25′ is increased as much as possible.
Patent Document 1: JP-A-2002-338801
Patent Document 2: JP-A-H09-205004